Superheterodyne receiver



' Sept. 27, 1938.

K. SCHLESINGER. 2,131,194 SUPERHETERODYNE RECEIVER Filed March 5, 1956 2Sheets-Sheet l F'iz Jaye/MW? Sept. 27, 1938.

K. SCHLESINGER 2,131,194 SUPERHETERODYNE RECEIVER Filed March 5, 1956 2Sheets-Sheet 2 Patented Sept. 27, 1938 UNETED STATES PATENT FriesSUPERHETERODYNE RECEIVER Kurt Schlesinger, Berlin, Germany, assignor. to

itadioaktiengesellschaft D.

Steglitz, Germany S. Loewe, Berlin- 10 Claims.

The present invention relates to receivers employing locally generatedoscillations and its main object is to prevent radiation of localoscillations, especially when the local oscillator operates on a shortor ultra-short wave.

- In such receivers there is considerable danger of radiation becausethe coupling capacity between electrodes of the mixing valve issufficient at very high frequencies to introduce a disturbing couplingbetween the antenna and the oscillator.

According to the invention, in a radio receiver employing locallygenerated oscillations for beating with oscillations collected by theantenna, radiation of the locally generated oscillations from theantenna is prevented by means of a neutralizing circuit.

Embodiments of the invention will now be described, by way of exampleonly, reference being made to the drawings comprising Figs. 1-4.

Fig. 1 shows diagrammatically the frequency changing circuit of asuperheterodyne receiver;

Fig. 2 is a more constructional embodiment employing a circuit similarto that of Fig. 1, and

Figs. 3 and 4 are modifications of the circuit of Fig. 1.

Reference will first be made to Fig. 1 which shows the frequencychanging circuit of a superheterodyne receiver comprising a mixing valve4 and an oscillatory valve 8; these two valves may be combined in asingle envelope. The antenna I is connected through a very smallcondenser 2 of about 1 cm. to the control grid 3 of the mixing valve 4whose cathode 5 is earthed. A screen grid 5 serves to screen the controlgrid 3 from the oscillation grid 1. Two or more screen grids may beprovided. Furthermore, a screen grid 32 may be arranged between anode 3|and oscillatory grid 1. This oscillation grid 1 is directly connected tothe grid (or alternatively the anode) of the triode 8. The triode 8,whose cathode 9 is likewise earthed, produces the local oscillations inconjunction with a circuit comprising condenser l and inductance ll. Thecircuit is so chosen that, in addition to the oscillation potentialapplied to electrode 1 of the mixing hexode 4, there is always present asmall oscillation potential which is opposite in phase to that of theformer.

Even when the'antenna is completely shielded from all other parts of thereceiver it still remains coupled to the oscillation circuit via theinter-electrode capacities of valve 4.

According to the applicants observations, the disturbing radiationproduced by superheterodyne receivers is primarily due. to the capacitybetween the control grid 3 and the oscillation grid 1. Owing to thepresence of the screen grid 6, this capacity amounts in practice to onlyabout 0.1 cm. In spite of this small value a disturbing radiation, whichincreases with increase in size of the antenna I, takes place when the,local oscillations are of very high frequency, e. g. in the case ofultra-shortwaves of 7 m. length the capacitive reactance of thiscondenser amounts only to 35,000 ohms.

This radiation may be reduced by employing two screen grids 6 and 6instead of one. This should, however, be regarded only as anapproximation to complete freedom from radiation. The supply conductor3' should be completely screened in the interior of valve 4'againstinternal coupling capacities by means of a shield l6.

A completeelimination of radiation without employing a secondscreen'grid t" is effected by applying a neutralizing oscillation to theantenna I. An adjustable fraction of p the oscillations produced bylocal'oscillator 8 and which is at reverse phase to that at grid I2, istaken through a very small adjustable condenser l8 and supplied to thecontrol grid terminal l9. The very small neutralization capacity I8 isadvantageously produced by a screened coupling condenser. An earthedplate I801; is inserted between the coupling plates of l8. y

The oscillator circuit valve 8' and oscillating circuit I0, ll may becompared with a capacitatively coupled three-point-circuit (the Germanterm is: Dreipunktschaltung) which represents a capacitativepotentiometer circuit by which incase of short waves the reverse phaseof auxiliary potential is best attained' The inherentearth capacities l3and M of the oscillat ing circuit I0, I l are authoritative for theanodecathode potential and the grid-cathode potential of valve 8; andthese operating potentials are opposed in phase. generally quite small(order of magnitude 10 cm.) the circuit can oscillate only at'highoperating frequencies; in case. of very high frequencies the required phaseopposition is attainedmost Since capacities l3 and M are accurately. Thestate of reverse phase between anode and grid of the oscillatory systemis also improved byconnecting the-anode supply consis of the frequencychanging stage of the receiver is made of metal and indicated by 20. Thechassis is closed on all sides and earthed. One plate of condenser I8 isconnected tothe oscillation circuit I0, I I which is located in theinterior of the oscillator box 20. The other plate of condenser I8 isconnected to the antenna I (either directly as shown in Fig. 2, or viacondenser 2 as shown in Fig. 1. In the latter case the value of thecoupling capacity I8 is greater). The grid choke coil 2| supplies gridbias to the control grid 3 through a very short conductor 22, and isalso connected to coupling condenser 2 and thus the antenna I. Theintermediate plate I8a of condenser I8 partly covers the aperture 35 inthe portion of the chassis separating the plates of condenser I8 and itsposition is adjusted by the screw 23. The neutralizing oscillations passthrough conductor 24 to antenna I. With complete shielding of I8 bymeans of I8a, the antenna I radiates on account of the harmful capacitybetween. the oscillation grid I and the control grid 3 alreadymentioned. By slowly increasing the effective aperture 35 in the uppersurface of 20 by moving the plate I8a, the coupling via condenser I8 isincreased until a point is found at which the radiation from the antennais neutralized.

After the neutralization adjustment has been found it is madeindependent of fluctuations and alterations of the partial capacities ofthe an tenna on the circuit by placing an earthed shield 25 over theentire circuit and leading the antenna connection in through a smallhole. All the battery feed conductors leading into the housing 2 areprovided with high frequency series chokes and earthing condensers.

The process of neutralizing by means of a reverse phase auxiliarypotential derived from the oscillator is not limited to the circuits ofFigs. 1 and 2. For example, the reverse phase potential may be produced,as shown in Fig. 3, by means of an auxiliary winding 26 which isinductively coupled to the oscillator coil II. .The auxiliaryoscillations obtained in this way will be exactly at reverse phase tothose applied to grid 3 via the inter-electrode capacity 29 so long asthe resonant frequency of winding 26 is higher than the oscillationfrequency of circuit I 0, II.- Also the tuning system which is connectedto the control grid 3, may be otherwise than as shown in Figs. 1 and 2.For example, as shown in Fig. 3, an oscillation circuit 27, 28 may beemployed for antenna tuning without disturbing the neutral izationbecause the neutralization is free from phase displacement. Also thecoupling of antenna I to grid 3 may be made inductive without disturbingthe action of the neutralizing process. Finally the neutralizingoscillations may also be introduced into the tuning circuit 27, 28 bymeans of an inductive coupling.

The invention is especially suitable for use in radio receiversoperating on ultra-short waves which may be modulated e. g. with speechcurrents or television signals.

I claim:

i. In a heterodyne receiver for the use in short wave art andultra-short wave art, means for preventing radiation of the locallygenerated oscillation by the receiver aerial, a mixing tube having acathode, a control grid, at least one screen grid, an oscillation grid,a second screen grid and an anode, arranged in the order named, anaerial circuit coupled with said control grid, an oscillatory tubehaving an anode, a cathode,

and a grid, a neutralizing circuit for compensating the undesiredcoupling between the controland oscillation-grid of said mixing tubeefiected by the inherent capacity between said two grids, saidneutralizing circuit consisting of a variable condenser connectedbetween the control grid of said mixing tube and the grid of saidoscillator tube so that a neutralizing potential of opposite phase withrespect to the original oscillatory potential is led from an electrodeof said oscillatory tube to the control grid of said mixing tube and theaerial circuit respectively the anode of said oscillator tube beingcoupled to the oscillation grid of said mixing tube.

2. In a heterodyne receiver for the use in short wave art andultra-short Wave art, means for preventing radiation of the locallygenerated oscillation by the receiver aerial, a mixing tube having acathode, a control grid, at least one screen grid, an oscillation grid,a second screen grid and an anode, arranged in the order named, anaerial circuit coupled with said control grid, an oscillatory tubehaving an anode, a cathode, and a grid, a neutralizing circuit forcompensating the undesired coupling between the controlandoscillation-grid of said mixing tube effected by the inherent capacitybetween said two grids, a variable neutralizing condenser connected inthe coupling circuit between the control grid of said mixing valve andthe anode or grid of said oscillator tube, so that a neutralizingpotential of opposite phase with respect to the original oscillatorypotential is led from the anode of said oscillatory tube to the controlgrid of said mixingtube and the aerial circuit respectively the controlgrid of said oscillatory tube being coupled to the oscillation grid ofsaid mixing tube.

3. In a heterodyne receiver for the use in short wave art andultra-short Wave art, means for preventing radiation of the locallygenerated oscillation by the receiver aerial, a mixing tube having acathode, a control grid, at least one screen grid, an oscillation grid,a second screen grid and an anode, arranged in the order named, anaerial circuit coupled with said control grid, an oscillatory tubehaving an anode, a cathode, and a grid, a neutralizing circuit forcompensating the undesired coupling between the controlandoscillation-grid of said mixing tube effected by the inherent capacitybetween said two grids, said neutralizing circuit consisting of avariable condenser connected between the control grid of said mixingtube and the anode of said oscillator tube so that a neutralizingpotential of opposite phase with respect to the original oscillatorypotential is led from an electrode of said oscillatory tube to thecontrol grid of said mixing tube and the aerial circuit respectively,the control grid of said oscillatory tube being coupled to theoscillator grid of said mixing tube, said neutralizing condenser beingconstructed as a screened condenser having a metal sheet which may beinserted between its two electrodes in more or less large extension.

4. In a heterodyne receiver for the use in short wave art andultra-short wave art, means for preventing radiation of the locallygenerated oscillation by the receiver aerial, a mixing tube having acathode, a control grid, at least one screen grid, an oscillation grid,a second screen grid and an anode arranged in the order named, an aerialcircuit coupled with said control grid, an oscillatory tube having ananode, a cathode, and a grid, a neutralizing circuit for compensatingthe undesired coupling between the controland oscillation-grid of saidmixing tube effected by the inherent capacitybetween said two grids,said neutralizing circuit consisting of a variable condenser connectedbetween the control grid of said mixing tube and the grid of saidoscillator tube, so that a neutralizing potentialof opposite phase withrespect to the original oscillatory potential is led from an electrodeof saidoscillatory tube to the control grid of said mixing tube and theaerial circuit respectively, the anode of said oscillator tube beingcoupled to -the oscillation grid of said mixing tube said oscillatortube and also said mixing tube with their appertain ing coupling elementbeing surrounded by' an earthed screening means, which is closed on allsides and within which all part-capacities are rendered invariable andout of-which there is passed only the aerial lead.

5. In a heterodyne receiver for the use in short,

wave art and ultra-short wave art, means -for preventing radiation ofthe locally generated oscillationby the receiver aerial, a mixing tubehaving a cathode, a control grid, at least one screen grid, anoscillation grid, a second screen grid and an anode arranged in theorder named, an aerial circuit coupled with said control grid, anoscillatory tube having an anode, a cathode, and a grid, a neutralizingcircuit for compensating the undesired coupling between the controlandoscillation-grid of said mixing tube effected by the inherent capacitybetween said two grids,

a variable neutralizing condenser connected between the control grid ofsaid mixing valve and the anode of said oscillator tube, so that aneutralizing potential of opposite phase with respect to the originaloscillatory potential is led from an electrode of said oscillatory tubeto the control grid of said mixing tube and the aerial circuitrespectively, said oscillator tube and also said mixing tube with theirappertaining coupling element being surrounded by an earthed screeningmeans, which is closed on all sides and within which all part-capacitiesare rendered invariable and out of which there are passed only theaerial lead and the feed lines, said feed lines are pro-,

vided with series chokes and are earthed capacitatively.

6. In a heterodyne receiver for the use in short wave art andultra-short wave art, means for preventing radiation of the locallygenerated oscillation by the receiver aerial, a mixing electrode systemhaving a cathode, a control grid, at least one screen grid, anoscillation grid, a, second screen grid and an anode, arranged in theorder named, an aerial circuit coupled with said control grid, anoscillatory electrode system having an anode, a cathode, and a grid, aneutralizing circuit for compensating the undesired coupling between thecontroland oscillation grid of said mixing electrode system effected bythe inherent capacity between said two grids, a variable neutralizingcondenser connected in the coupling circuit between the control grid ofsaid mixing electrode system and the anode of said oscillator electrodesystem, so that a neutralizing potential of opposite phase with respectto the original oscillatory potential is led from an electrode of saidoscillatory electrode system to the control grid of said mixingelectrode systemand the aerial circuit respectively, the control grid ofsaid oscillatory tube being coupled to the oscillation grid of saidmixing tube, said oscillator electrode system and the electrode of themixing electrode system are arranged in the same tube.

'7. In a heterodyne receiver for the use in short wave art andultra-short wave'art, means for preventing radiation of the locallygenerated oscillation by the receiver aerial, a mixing tube having acathode, a control grid, at least one screen grid, an oscillation grid,a second screen grid and an anode, arranged in the order named,

an aerial circuit coupled with said'control grid, an oscillatory tubehaving an anode, a cathode, and a grid, a neutralizing circuit forcompensating the undesired coupling between the controlandoscillation-grid of said mixing tube effected by the inherent capacitybetween said two grids,

a variable neutralizing condenser connected in r the coupling circuitbetween the control-grid of said mixing tube and the grid of saidoscillator tube, so that a neutralizing potential of opposite phase withrespect to the original oscillatory potential is led from'the anode ofsaid oscillatory tube to the control grid of said mixing tube and theaerial circuit respectively, the anode of said oscillatory tube beingcoupled to the oscillation grid of said mixing tube, said neutralizingcondenser being constructed as a screened condenser having a metal sheetwhich may be inserted be tween its two electrodes in more or less largeextension.

8. In a heterodyne receiver for the use in short wave art andultra-short wave art, means for preventing radiation of the locallygenerated oscillation by thereceiver aerial, a mixing tube having acathode, a control grid, at least one screen grid, an oscillation grid,a second screen grid and an anode, arranged in the order named,

an aerial circuit coupled with said control grid,

an oscillatory tube having an anode, a cathode, and a grid, aneutralizing circuit for compensating the undesired coupling between thecontroland oscillation-grid of said mixing tube effected by the inherentcapacity between said two grids, said neutralizing circuit consisting ofa variable condenser connected between the control grid of said mixingtube and the anode of said oscillator tube so that a neutralizingpotential of opposite phase with respect to the original oscillatorypotential is led from an electrode of said oscillatory tubetothe controlgrid of said mixing tube and the aerial circuit respectively, thecontrol grid of said oscillatory tube being coupled to the oscillationgrid of said mixing tube,

said neutralizing condenser being constructed as a screened condenserhaving a metal sheet which may be inserted between its two electrodes inmore or less large extension, said oscillator tube and also said mixingtube with their appertaining circuit elements being surrounded by anearthed screening means, which is closed on all sides and within whichall part-capacities are rendered invariable and out of which there ispassed only the aerial lead.

9. In a heterodyne receiver for the use in short wave art andultra-short wave art, means for preventing radiation of the locallygenerated oscil lation by-the receiver aerial, a mixing tube having acathode, a control grid, at least one screen grid, an oscillation grid,a'second grid and an anode, arranged in the order named, an aerialcircuit coupled with said control grid, an oscillatory tube having ananode, a cathode, and'a grid,

a neutralizing circuit for compensating the uning tube and the grid ofsaid oscillator tube so that a neutralizing potential of opposite phasewith respect to the original oscillatory potential is led from anelectrode of said oscillatory tube to the control grid of said mixingtube and the aerial circuit respectively, the anode of said oscillatortube being coupled to the oscillation grid of said mixing tube, saidoscillator electrode systern and the electrode of the mixing electrodesystern are arranged in the same tube.

10. In a heterodyne receiver for the use in short wave art andultra-short wave art, means for preventing radiation of the locallygenerated oscillation by the receiver aerial, a mixing tube having acathode, a control grid, at least onescreen grid, an oscillation grid, asecond screen grid and an anode arranged in the order named, an aerialcircuit coupled with said control grid, an oscillatory tube having ananode, a cathode, and a grid, a neutralizing circuit for compensatingthe undesired coupling between the controland oscillation-grid of saidmixing tube effected by the inherent capacity between said two grids,said neutralizing circuit consisting of a variable condenser connectedbetween the control grid of said mixing tube and the grid of saidoscillator tube so that a neutralizing potential of opposite phase withrespect to the original oscillatory potential is led from an electrodeof said oscillatory tube to the control grid of said mixing tube and theaerial circuit respectively, the anode of said oscillator tube beingcoupled to the oscillation grid of said mixing tube, said oscillatortube and also said mixing tube with their appertaining circuit elementsbeing surrounded by an earthed screening means, which is closed on allsides and within which all part-capacities are rendered invariable andout of which there is passed only the aerial lead and the feed lines,said feed lines are provided with series chokes and are earthedcapacitatively.

, V KURT SCHLESINGER.

